The negotiator, Masanori Miyahara, said in a telephone interview this week that Japan “would have no choice but to take a reservation” — in effect, to ignore the ban and leave its market open to continued imports — if the bluefin tuna were granted most-endangered species status.

“It’s a pity,” he said, “but it’s a matter of principle.”

Mr. Miyahara, Japan’s top delegate to the United Nations Convention on International Trade in Endangered Species of Wild Fauna and Flora, referred to as Cites, said the convention was the wrong forum for managing the fishing of the bluefin tuna.

A formal proposal for a ban — which requires the approval of two-thirds of its 175 member countries — is scheduled to be presented at a Cites meeting next month in Doha, Qatar.

The position of Japan, which consumes about 80 percent of the bluefin tuna caught in the Mediterranean, “is very simple,” Mr. Miyahara said. He said Japan believed that a different organization, the International Commission for the Conservation of Atlantic Tunas, known as Iccat, should manage bluefin tuna catches and protection.

Mr. Miyahara said Japan acknowledged that the bluefin tuna needed protection, but the endangered-species convention was “quite inflexible,” he said.

Historically, he said, almost no species added to the Cites endangered species list had ever been removed. “We don’t believe the bluefin tuna is endangered to that extent,” he said.

Meanwhile, Europe appeared to be moving to a compromise.

France, home of the largest Mediterranean bluefin fleet, said on Feb. 3 that it was prepared to back an international trade ban at the Cites meeting, to take effect after 18 months. But a person with knowledge of the European Commission’s thinking who asked not to be identified because the commission had not formally adopted the position, said on Friday that officials were planning to propose that Iccat be given a last chance to give depleted stocks of the tuna a chance to recover by temporarily banning all commercial trade in the fish.